Cancel Starz Subscriptioin

I accidentally used the flex box to purchase a Starz subscription. I want to cancel that since I saw it come up at a $8.99 charge on my Xfinity internet bill. It's really frustrating because there is no way to manage/ do this on the xfinity portal, and the flex box doesn't show me subscribed to anything, so I can't do this anywhere. Xfinity, I don't care about reversing any charges/payments for using the Starz subscription. But you must create an intelligible way of canceling these subscriptions! We've had this for over a week, so the "give it time to show up on the record" excuse doesn't cut it.

PS. I wouldn't have ever chosen to use Xfinity if they weren't the only internet option in my area.